d meson production in au+au collisions at ๐ =๐๐๐ gev measured ...heavy flavor tracker....
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Dยฑ meson production in Au+Au collisions at ๐๐ต๐ต = ๐๐๐GeV measured by the STAR experiment
Jakub Kvapil, for the STAR CollaborationFaculty of Nuclear Sciences and Physical Engineering
Czech Technical University in Prague
AbstractCharm quarks are mainly created in hard processes at the beginning of heavy-ion collisions and can be used as a tool to study properties of the Quark-Gluon Plasma (QGP). The modification to D-meson production in heavy-ioncollisions is sensitive to the energy loss of charm quarks in the QGP. The Heavy Flavor Tracker was installed at the STAR experiment in 2014 and enables the topological reconstruction of the decay vertices for open charmmesons. It significantly improves precision on charm meson measurements. Besides the measurement of D0, Dยฑ provides an additional handle and cross-check to study the interaction between charm quarks and the medium. Inthis poster, we present measurements of Dยฑ production in Au+Au collisions at sNN = 200 GeV. Dยฑ mesons are reconstructed topologically via the hadronic decay channel Dยฑ โKโฯยฑฯยฑ from the data collected in 2014 with theHeavy Flavor Tracker. The invariant yield of Dยฑ mesons in the transverse momentum range of 2 < pT < 10 GeV/c is extracted for 0-10% most central Au+Au collisions, and is found to be consistent with the D0 yield.
The STAR Collaboration
drupal.star.bnl.gov/STAR/presentations
Results
Acceptance and reconstruction efficiency
Conclusion
Dยฑ raw yields
Dยฑ three body decay, DCApair (blue lines), ฮmax (red lines).
References[1] G. Xie, for the STAR Collaboration, Nuclear Physics A, Volume 956, Pages 473-476
[2] J. Schambach, for the STAR Collaboration, Physics Procedia, Volume 66, 2015, Pages 514-519
[3] L. Adamczyk, for the STAR Collaboration, arXiv:1701.06060 [nucl-ex]
This work was supported by the grant LG15001 and LM2015054 of Ministry of
Education, Youth and Sports of the Czech Republic.
Dยฑ reconstruction
โข About 900 million minimum-bias Au+Au events at sNN =
200 GeV recorded in year 2014 are used for this analysis.
โข Event selection cuts:
โข Vertex position |Vz| < 6 cm
โข Vertex correlation |Vz(VPD)-Vz| < 3 cm.
โข Track selection cuts:
โข Hits in the two PIXEL and one IST layers are required.
โข At least 20 space points in the TPC for track
reconstruction.
โข Pseudo-rapidity: ฮท < 1.
โข Topological cuts:
โข Daughter DCA to primary vertex: DCAฯ > 100 ฮผm,
DCAK > 80 ฮผm.
โข Pointing angle of reconstructed vertex to primary
vertex: cos(ฮธ) > 0.998.
โข Dยฑ decay length between 30 ฮผm and 2000 ฮผm (PDG cฯ
= 311.8 ฮผm).
โข DCA between daughter pairs: DCApair< 80 ฮผm.
โข Longest edge of the triangle formed by reconstructed
daughter pair vertices must fulfil ฮmax < 200 ฮผm.
โข Particle identification:
โข Daughter pT > 500 MeV/c.
โข TPC: |nฯฯ| < 3.0 for pions and |nฯK| < 2.0 for kaons.
โข TOF: |1/ฮฒ-1/ฮฒฯ| < 0.03 for pions and |1/ฮฒ-1/ฮฒK| < 0.03
for kaons. TOF information is used when available,
otherwise only TPC is used.
Motivation
Nuclear modification factor (RAA) [1].
โข Heavy quarks are mostly created in the
initial phase of heavy-ion collisions.
Therefore they experience the entire
evolution of the system and are a good
probe to study the properties of the
Quark-Gluon Plasma (QGP).
โข The strong suppression of high-pT D0
meson yields indicates large energy loss
of charm quarks in the QGP.
โข Besides the D0 meson, Dยฑ provides an
independent handle to study the charm
quark interaction with the medium.
STAR detector
Heavy Flavor Detector (2014-2016)
Time Projection Chamber Time Of Flight
Magnet
Muon TelescopeDetector (2014)
Barrel ElectroMagneticCalorimeter
Vertex PositionDetector
STAR detector with main mid-rapidity detectors. HFT resolution [3].
โข The Solenoidal Tracker at RHIC (STAR) was designed to investigate the strongly
interacting matter. It covers full azimuth at mid-rapidity ( ฮท < 1) with 0.5 T of solenoidal
magnetic field.
โข Main sub-detectors used in this analysis are:
1. Time Projection Chamber (TPC): main tracking device, particle identification via
specific energy loss dE/dx, momentum reconstruction.
2. Time Of Flight (TOF): low pT particle identification via velocity 1/ฮฒ.
3. Heavy Flavor Tracker (HFT) [2]: new inner tracking system composed of three silicon
detectors โ the PIXEL made of two Monolithic Active Pixel Sensors layers,
Intermediate Silicon Tracker (IST) and Silicon Strip Detector (SSD).
ฮmax
DCApair
โข The Hadronic decay channel
Dยฑ โKโฯยฑฯยฑ is used.
โข Background is estimated via the
wrong-sign method: 2 correct-
signal (D+, D-) and 6 wrong-signal
(background) combinations.
โข Dยฑ raw yields and significance are
calculated using the bin-counting
method in the 0-10% central
Au+Au collisions for 2 < pT < 10
GeV/c.
โข Significance:๐ ๐๐๐๐๐
๐ ๐๐๐๐๐+๐๐๐๐๐๐๐๐ข๐๐
โข Data-driven fast simulator has been
developed using
1. centrality-dependent Vz distributions
from data
2. ratio of HFT matched tracks to TPC
tracks from data
3. TPC efficiency and momentum
resolution from embedding
and validated with full GEANT simulation.
โข The Dยฑ raw yield is corrected using the following formula:
โขd2๐
d๐๐d๐ฆ
1
2๐๐๐=
๐๐๐๐๐๐ข๐๐๐๐๐๐๐๐ก๐๐
2โ๐โ๐๐โ๐๐๐๐โ๐๐๐ฃ๐๐๐ก๐ โ๐ต๐ โ๐๐โโ๐๐โโ๐ฆโ๐ธ๐๐ ๐๐
where Ncharge = 2, Nevents number of events, BR = (9.13ยฑ0.19)%, ฮpT bin width, ฮy
rapidity width, Eff(pT) detector acceptance x efficiency.
โข Systematic uncertainties are estimated by varying cuts on daughter pT, daughter DCA,
DCApair, ฮmax, TPC fit points, changing histogram binning and testing fit stability.
โข The D0 spectrum in p+p collisions measured using 2009 data is used as the baseline.
โข The Dยฑ invariant yield spectrum in 0-10% central Au+Au collisions at sNN = 200 GeV is
measured via the hadronic decay channel Dยฑ โKโฯยฑฯยฑ for the pT range of 2-8 GeV/c.
โข The Dยฑ and D0 yields are consistent, both indicating strong energy losses of charm
quarks in the medium.
โข The invariant yield of Dยฑ mesons with 2 < pT < 8 GeV/c in 0-10% central Au+Au
collisions is consistent with that of D0 mesons within uncertainties. The nuclear
modification factor (RAA) for Dยฑ also exhibits strong suppression at high pT, indicatingsubstantial energy loss of charm quarks in the medium.
Ncol uncert.
ฯpp uncert.
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